<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title></title>
</head>
<body>
<h1>
    show "Hello" after 3 when your click button!
</h1>
<hr>
<button onclick="functionForButton()">
    Click Me!
</button>

<script>
    function functionForButton() {
        setTimeout(function () {
            alert("Hello")
        }, 3000)
    }
</script>
</body>
</html>